This invention relates to a downconverter and more particularly to a television channel converter that changes television broadcasting channels in the UHF or SHF band to VHF television channels.
In the United States, a television channel, for example, the 2150 MHz to 2156 MHz channel slot is conventionally frequency-converted to VHF television channels such as channel 3 (60 to 66 MHz) or channel H (162 to 168 MHz) for reception by an ordinary television receiver. In such a case, a local oscillator of the downconverter operates at 2216 MHz or 2318 MHz. The requirement for the frequency drift of the local oscillator is .+-.100 KHz irrespective of the operating frequency and is fairly strict.
Therefore, a stable crystal oscillator for producing a reference frequency signal and means for multiplying the frequency of the crystal oscillator up to a required frequency are used for a stabilized local oscillator signal source. However, a crystal oscillator is unsuitable for frequency changes, and the required use of a multistage frequency multiplying circuit, necessitated by the use of a crystal oscillator, is known to have an operation limit of about 120 MHz and suffers from disadvantages in that spurious signal produced from each stage interfere with input signals or are radiated from an antenna terminal.